1. Field of the Invention
The present invention relates to airfoils used in gas turbine engines, and more specifically to measuring the pressure drop across cooling holes on the airfoil to determine if the inner cavity for cooling air passage is properly designed.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Gas turbine engines use blades and vanes with cooling air passages therein to prevent the airfoils from degrading due to extreme temperatures. These airfoils include film cooling air holes leading from the internal cooling air passages onto the outer surfaces of the airfoils to provide a blanket of cooling air over the airfoil surface, and therefore allowing for highest gas turbine temperatures.
When designing a turbine airfoil, the airflow through the internal cooling passages and the film cooling holes is critical. Too much airflow will result in a waste of cooling air flowing into the gas stream. Too little airflow and the airfoil will lack adequate cooling. It is very important during the design stage to properly size the cooling passages before the blade or vane is put into operation in the gas turbine engine.
The gas turbine industry relies upon processes that measure air pressure within various turbine components (typically blades or vanes). The methods being used to obtain these pressures aren't necessarily standardized. This may be intentional dependent upon the objective, but it has been observed that some manufacturers use methods that do not provide reliable, consistent results. This can lead to problems ranging from one part being rejected up to a situation whereby an engine design is significantly flawed due to erroneous calculations obtained through inadequate methodology or tools. This application addresses the issue.
The method currently used in the prior art involves a pressure measurement device that inserts a small hypodermic tube within one of the turbine components film cooling holes. These holes can vary in size, shape and location. The problem is that the “hypo” tube penetrates internally to varying depths and angles. This method becomes highly subjective to error because of the many dynamic conditions that affect the reading. It would be ideal to get a “static” pressure measurement in these instances. Also, the sealing of the air around the “hypo” tube may be insufficient, thereby contributing to erroneous data as well.